Modernize, refine, and standardize the notebook collection

[sis0k0]

Overview

This PR is a broad maintenance and quality pass over the notebook collection, focused on notebooks/agents/. It normalizes install commands, cleans up cell outputs, adds "Open in Colab" buttons, standardizes environment-variable handling, migrates notebooks to the current Atlas vector index syntax, fixes dead links, and substantively refines several individual agent notebooks. 35 files changed.

Deeply refined notebooks

Substantive content and narrative rewrites, not just mechanical edits:

• agent_fireworks_ai_langchain_mongodb.ipynb: Fully modernized the Fireworks + LangChain agent, with refreshed narrative, reworked setup, and updated code.
• ai_agent_with_pydanticai_and_mongodb.ipynb: Refined the Pydantic AI + MongoDB agent (~2,000 lines reworked).
• agentchat_RetrieveChat_mongodb.ipynb: Refined the AutoGen AgentChat / RetrieveChat walkthrough.
• agentic_rag_factory_safety_assistant_with_langgraph_langchain_mongodb.ipynb: Compatibility fixes and deprecation-warning cleanup (~1,900 lines), plus an expanded intro and problem statement.
• airbnb_agent_openai_llamaindex_mongodb.ipynb: Refined narrative and setup.

Standardized environment-variable handling

The five modernized notebooks now load secrets consistently:

• Add python-dotenv to the install cell and call load_dotenv() so variables defined in a local .env file are read automatically.
• Introduce a shared get_or_prompt_env(var_name, prompt_text) helper that returns the value from the environment (.env or already-set) when present, and otherwise falls back to a getpass prompt, raising a clear EnvironmentError if left empty.
• Keys such as OPENAI_API_KEY, FIREWORKS_API_KEY, and MONGODB_URI are resolved through this helper instead of being hardcoded or prompted ad hoc, so the notebooks run non-interactively when a .env file is present and prompt gracefully when it is not.

Other standardized conventions

Applied consistently across the agent notebooks:

• Install commands: Replaced !pip with %pip, then normalized all installs to %pip install -U -q for quiet, up-to-date installs.
• Cell outputs: Cleared noisy pip-install outputs.
• Open in Colab: Added launch buttons to all notebooks across agents/, rag/, evals/, and partners/.
• Intro sections: Added consistent titles and problem statements to ~15 agent notebooks.

Modernization

• Atlas vector index syntax: Migrated the remaining notebooks (advanced retrieval techniques + LangChain, multimodal Atlas vector store, POLM AI Stack) to the current syntax.

Housekeeping

• Dead-link fixes: Patched broken links in langchain_parent_document_retrieval.ipynb, the multimodal Atlas notebook, and the Haystack cooking-agent notebook.
• .gitignore: Added one entry (to keep local .env files out of version control).